MIG welding is the process most people learn first, and for good reason. The wire and the shielding gas both feed through one gun, so you aim, squeeze the trigger, and steer, instead of juggling a separate filler rod with your other hand.
This guide takes you from a cold machine to a finished bead on mild steel. You will check the welder over, set the gas, grind the joint clean, dial in voltage and wire speed, tack the parts, and run your first pass.
Prep and settings do most of the work here. Get those two right and the rest is hood time. Grab some scrap steel and follow along.
Key Takeaways
- MIG welding (GMAW) feeds a continuous wire electrode and shielding gas through one gun, which makes it the easiest arc process for a beginner to learn.
- Mild steel usually welds between 15 and 21 volts, and a common current rule of thumb is 1 amp for every 0.001 inch of steel thickness.
- Grind the joint to bright bare metal 1 to 2 inches past the weld line, because contamination is the leading cause of weld porosity.
- Run shielding gas around 20 to 25 cubic feet per hour indoors, and wear an auto-darkening helmet, leather gloves, and flame-resistant clothing every time you strike an arc.
What Is MIG Welding?
MIG stands for Metal Inert Gas welding. The technical name is Gas Metal Arc Welding (GMAW), but everyone in the shop calls it MIG.
It creates an arc between a continuously fed wire electrode and the base metal. This melts the wire and the base metal to form a pool. A shielding gas flows through the gun simultaneously to protect the molten pool from atmospheric contamination.
MIG welding is versatile. It bonds mild steel, stainless steel, and aluminum. It creates clean welds on thin sheet metal and heavy structural plates alike. Because of this versatility, MIG accounts for over 50 percent of all industrial metal welds (1).
How Does MIG Welding Work?
MIG welding works by completing an electrical circuit between the feeding wire and the steel you are joining. You clamp the ground lead to the workpiece or a clean metal table, and when you squeeze the trigger the wire feeds out, touches the metal, and strikes an arc.
This short circuit generates intense heat. The wire melts and deposits into the joint, acting as a filler material. At the same time, the gas nozzle directs a shield of inert gas (usually Argon and CO2) around the arc. This gas creates a barrier that stops oxygen and nitrogen from weakening the weld.
A quality MIG weld has even ripples and smooth edges. It should look like a “stack of dimes” knocked over.
Advantages of MIG Welding
- High travel speeds and efficiency.
- Easier to learn than Stick or TIG.
- Works on a wide range of metal thicknesses.
- Produces minimal slag and cleanup.
- Great for long, continuous welds.
Disadvantages of MIG Welding
- Requires a shielding gas bottle (harder to transport).
- Sensitive to wind (blows away shielding gas).
- Initial setup cost can be higher due to gas.
- Risk of “cold lap” if penetration isn’t deep enough.
- Bulky torch can be hard to use in tight spaces compared to TIG welding.
What Do You Need to MIG Weld?
You need a MIG welder and gun, a shielding gas cylinder, mild steel wire, a ground clamp, an angle grinder, and full protective gear. Gear comes first, because a MIG arc throws UV radiation, molten metal, and live electrical current at you.
- Auto-Darkening Helmet: Essential for protecting your eyes from arc flash.
- Welding Gloves: Heavy-duty leather MIG gloves protect hands from heat and spatter.
- Welding Jacket: Flame-resistant cotton or leather to prevent burns.
- Respirator: A welding respirator matters in small spaces or when welding coated metals.
- Leather Boots: Enclosed work boots prevent hot sparks from burning your feet.
- Safety Glasses: Wear these under your helmet for grinding protection.
Once you are safe, gather your gear.
- MIG Welder with gun/torch.
- Gas Cylinder (75% Argon / 25% CO2 is standard for steel).
- Welding Wire (ER70S-6 is common for mild steel).
- Ground Clamp.
- Wire Cutters/Pliers.
- Angle Grinder (for prep).
How Do You MIG Weld Step by Step?
You MIG weld by inspecting the machine, connecting gas, grinding the joint to bare metal, setting voltage and wire speed, tacking the parts, then running a steady bead and letting it cool. The 17 steps below cover a lap or butt joint in mild steel, and the setup half matters as much as the trigger-pulling half.
1. Machine Inspection
Open the side door of your welder. Check the wire spool. It should be secured with the tension nut but free enough to rotate. Ensure the wire sits correctly in the drive roll grooves.
If you are using solid wire, you need gas. If you are using flux-cored wire (gasless), ensure your polarity is set correctly according to the machine’s chart (usually DCEN).
2. Connect the Gas
Secure your gas cylinder chain to the cart or wall so it cannot tip over. Connect the regulator and hose. Open the main tank valve gently. Stand to the side, not directly in front of the gauges.
Squeeze the trigger on the torch to get gas moving, then set the regulator. According to ESAB, MIG work indoors usually runs about 20 to 25 cubic feet per hour measured at the nozzle, and that range covers almost every DIY job. Turning it higher wastes gas and can pull air into the puddle instead of shielding it.
3. Check the Torch and Tip
Inspect your contact tip. It should match your wire diameter (e.g., 0.030″ tip for 0.030″ wire). If the tip is worn out or oval-shaped, replace it. Ensure the nozzle is clean and free of spatter buildup.
4. Secure the Ground Clamp
A bad ground causes sputtering and poor welds. Attach the clamp directly to your workpiece or a clean metal welding table. Do not attach it over rust or paint. Grind a clean spot for the clamp if necessary.
5. Prep the Metal
This is the step beginners rush, and it is the one that decides whether the bead comes out solid. Oil, rust, paint, mill scale, and moisture are the leading cause of weld porosity, because they stop the wire’s deoxidizers from scavenging the gases in the air (2). Per Hobart Brothers, you should grind or wire-brush the joint back to bright bare metal 1 to 2 inches on either side of the weld line before striking an arc. Finish with an acetone wipe to lift the oil a grinding wheel just smears around.
6. Clear the Area
Sparks can fly up to 35 feet. Remove sawdust, rags, gas cans, and plastic from your work zone. Keep a fire extinguisher nearby properly rated for electrical and chemical fires.
7. Gear Up
Put on your jacket, boots, and gloves. Adjust your helmet settings. For MIG welding steel, a shade setting between 10 and 12 is usually appropriate depending on the amperage.
8. Set Voltage and Wire Speed
Most MIG welders have a chart inside the door. Find your metal thickness (gauge) and your wire diameter on the chart.
Set the voltage (heat) and wire feed speed (amperage) to the recommended numbers. Think of voltage as the width and fluidity of the puddle, and wire speed as the penetration and fill.
For mild steel, voltage usually lands between 15 and 21 volts, near the bottom of that range on thin sheet and near the top on quarter-inch plate (3). If your machine reads in amps instead, the rule of thumb per Miller Electric is roughly 1 amp for every 0.001 inch of steel thickness, so 1/8-inch plate wants about 125 amps. Treat both as a starting point, then run a test bead on scrap of the same thickness and adjust by sound.
9. Adjust Stickout
“Stickout” is the length of wire protruding from the contact tip. For the short-circuit transfer most beginners run, trim the wire so about 1/4 to 3/8 inch sticks out, per Miller Electric. Longer stickout adds resistance, drops current at the arc, and makes the puddle sputter. Too short and you risk fusing the wire to the tip or burying the nozzle in spatter.
10. Body Position
Get comfortable. Use two hands on the gun for stability. Rest your hip against the table or brace your arm if possible. A steady hand creates a steady bead.
11. Tack Weld the Joint
Don’t weld the whole seam yet. Heat causes metal to expand and warp. Place small “tack” welds at the ends and center of your joint to hold everything in alignment. Check your squareness before committing to the full weld.
12. Start the Arc
Lower your helmet. Position the wire at the start of the joint. Squeeze the trigger.
Listen to the sound. A good MIG weld sounds like frying bacon, a consistent, violent crackle.
- Hissing sound: Voltage is too high or wire speed is too slow.
- Loud popping/stuttering: Voltage is too low or wire speed is too fast.
Pro Tip
13. Push or Pull?
The direction matters.
- Pushing (Forehand): The torch angles forward, creating a flatter bead with less penetration. Good for thin metal.
- Pulling (Backhand): You drag the puddle. This creates a taller bead with deeper penetration. This is generally preferred for steel.
Keep your gun angle at about 10 to 15 degrees from vertical either way. A push angle also buys better visibility ahead of the arc, less spatter, and better gas coverage on flat and horizontal welds, which is why it suits thin sheet.
14. Watch the Puddle
Ignore the sparks; watch the molten orange puddle. Move the torch at a steady speed. If you move too fast, the weld will be thin and weak. If you move too slow, you might burn through the metal.
You can move in a straight line (stringer bead) or use a slight motion like a cursive “e” or a zig-zag to tie the toes of the weld into the metal.
15. Finish and Inspect
Release the trigger at the end of the joint and hold the gun in place for a second. The post-flow gas protects the weld while it solidifies.
Inspect the weld. It should have no holes (porosity) and the edges should blend smoothly into the base metal.
16. Shut Down Safety
Turn off the gas cylinder first. Squeeze the trigger to bleed the remaining gas from the line. Then, turn off the machine.
17. Let It Cool
Metal stays hot for a long time. Don’t touch it with bare hands. Let it air cool naturally. Quenching it with water can make the steel brittle.
How Do You Get Cleaner MIG Welds?
Cleaner MIG welds come from bare metal, a steady travel speed, and a wire that feeds without stuttering. The five habits below fix most of what goes wrong once you can already lay a bead.
Listen to the Bacon
Sound is your best diagnostic tool. If the arc sounds erratic, stop. Check your ground clamp and your settings. If it sounds like a machine gun, your wire speed is too high. Dial it in until you hear that steady sizzle.
Cleanliness is King
MIG welding hates contaminants. Mill scale, the grey flaky layer on new hot-rolled steel, is an insulator, so grind it off rather than trying to burn through it. Weld over paint or rust and the arc wanders while the bead fills with gas pockets. Keep a dedicated flap disc for prep so you are not dragging grinding dust from another job into the joint.
Watch Your Contact Tip
Spatter can build up inside the nozzle and block gas flow. Buy a pair of “welper” pliers to ream out the nozzle occasionally. Apply nozzle gel (dip the hot tip into it) to prevent spatter from sticking.
Get Comfortable
Don’t do the “death grip.” Holding the gun too tight makes your hand shake. Relax your grip. Imagine you are drawing a line with a large marker.
Manage the Cord
Keep the gun cable as straight as possible. If the cable is coiled tightly or kinked, the wire liner creates friction. This causes the wire feed to surge and stutter.
FAQs
Job Weld Done
MIG welding pays you back quickly. Lifting your hood on a clean, even bead you laid yourself is a good feeling, and it opens up automotive repair, gate and railing work, shop fixtures, and metal art.
Expect the first few beads to look rough. Scrap steel is cheap, so burn through a pile of it before you weld anything that matters. Set your gas, grind the joint, dial the chart numbers in, and let the sound tell you what to change.
